1 Hagfish are rule-breakers. They do not obey the rules of the physical features found in most fish species. For example, their bodies are smooth; they don't have scales like many other fish. Their skeletons are made of cartilage, not bone. They lack jaws. It is true that there are plenty of other fishes that also break the first two rules. Eels, swordfish, and catfish are all scale-less. Sharks, rays, and skates all trade true bones for cartilage. The third trait, however, is what makes hagfish stand out. They are classified by scientists as jawless fish. Lampreys are the only other fish sharing that same bizarre characteristic as hagfish.2 Hagfish have long, slender bodies. They measure 16-32 inches long. Their eyes, located under their skin, are simple, leaving them virtually blind. To compensate for eyesight, they have well-developed senses of smell (their single nostril) and touch (the four pairs of tentacles around their mouths) that permit them to search for food as they travel along the murky seabed. Hagfish dine on bristle worms and other marine invertebrates. They also eat dead or dying fish – the two food items that make hagfish infamous! Of course, many animals devour carrion or attack the wounded. Vultures, Komodo dragons, and Tasmanian devils all do that. Nevertheless, none of them choose to bore inside their prey and consume it inside out with their rasping tongues (plate-like structures bearing two rows of horny teeth). As horrifying and gross as it sounds, this is exactly what hagfish do!3 Aside from their rather unusual anatomy and dining behaviors, hagfish are excellent contortionists. They can tie themselves into knots and pass those loops down along their bodies. This skill is very useful when they try to pull off flesh from a carcass, to avoid capture, and to clean off mucus. Mucus? Yes, that's another unique thing about hagfish. When threatened, they produce large amounts of slime to deter would-be predators. As soon as the danger passes, they carry out this trick to wipe slime away. Because of their ability to excrete mucus and their eel-like shape, hagfish are also called "slime eels."